The present invention relates to measurement of liquid in fluid reservoirs, and more particularly, to measurement of lubricating oil in an oil reservoir of a gas turbine engine.
In many gas turbine engines, the amount of oil of an oil reservoir is measured using a floatable magnet near a reed switch array that includes a resistor ladder. Depending on the depth of oil, a particular reed switch will be closed by the magnet, sending current through the resistor ladder. The output of such a device is discrete with resolution limited by the spacing between and length of the reed switches. Alternatively, a linear variable differential transducer (LVDT) can provide an analog output and does not require a multitude of switches. However, LVDT's are typically large and bulky—at least two to three times taller than the measureable range of the device.